Those of us that have set up a PA system for a gig (or watched on as another engineer did the same) are probably familiar with the principle of equalizing the room. The basic principle is to use a graphic equalizer to adjust the output of the PA to counteract the notches and boosts in the various frequencies due to the size and shape of the room.

Of course we can also accomplish this in digital audio, however the process is not quite as straightforward as we might expect. One of the main issues with using a digital system, which creates a filter to invert the impulse response is that such a system will only be valid for the specific measurement point. Move even a few millimeters and the ‘corrected’ audio may sound worse. A more balanced approach is therefore required, which will sound ‘better’ at more locations in the room, despite being less correct at the measurement point. Michael Gerzon’s 1991 paper discusses in detail digital room correction.